And what makes it easy to stack shields? These do! Our FPin6L-413. Catchy name, right?

It's a female socket strip, 6 positions long, with a Long modification of 0.0413" tail. See?

In short, you solder these in where the standard Arduino Shield interface pins would go, but now you also have a matching set of female sockets on top! Use them for stacking more shields, or just as convenient test-measurement points for your probes.